Naturally occurring low quality sour gas reservoirs exist which contain, in addition to methane and other hydrocarbons, significant quantities of carbon dioxide and hydrogen sulfide. Such reservoirs have sometimes not been produced because of the expense of recovering hydrocarbon and other stream(s) meeting sales specifications and environmental requirements. Developments in recent years include carbon dioxide miscible flooding to facilitate enhanced oil recovery from certain reservoirs. Such carbon dioxide miscible flooding requires sources of large quantities of carbon dioxide, and if the carbon dioxide is to be transported over significant distances, the carbon dioxide should be substantially free of hydrogen sulfide to meet environmental regulations. Accordingly, efficient and economical processes for producing sweet high purity carbon dioxide and hydrocarbon streams meeting sales specifications and environmental requirements from such naturally occurring low quality sour natural gas reservoirs are highly desirable.
In addition, during the production of a reservoir by carbon dioxide miscible flooding it is known that after a time carbon dioxide breakthrough occurs, i.e., carbon dioxide appears in the produced fluids in significant quantities. Gaseous streams derived, for example, from wellhead separator(s) of such carbon dioxide miscible flood produced reservoirs can, therefore, have compositions similar to gas produced from naturally occurring low quality reservoirs, for example, high levels of carbon dioxide and significant amounts of hydrogen sulfide and hydrocarbons.
Typically, processing the above gases can involve sulfur recovery, usually by the Claus reaction. When the acid gas feed stream to the sulfur recovery facility contains 10 to 15 mol percent H.sub.2 S or greater, the sulfur recovery can be carried out using Claus technology involving a furnace and/or one or more Claus reactors. For example, for acid gas feeds containing 40 to 50 mol percent H.sub.2 S or greater, a straight through design Claus plant can be utilized; and, for feeds containing 40 to 50 mol percent H.sub.2 S down to about 10 to 15 mol percent H.sub.2 S, a split flow design Claus plant can be utilized. When the gaseous feeds are leaner in H.sub.2 S, however, specialized designs must be utilized. Accordingly it is desirable in design of gas processing facilities to provide a Claus plant feed having greater than 10 to 15 mol percent H.sub.2 S, thereby avoiding the use of the less efficient specialized designs.
Consequently, there is a continuing need for processes for treating gaseous streams containing significant quantities of CO.sub.2 and H.sub.2 S, in addition to hydrocarbons, which can economically produce sweet CO.sub.2 and hydrocarbon product streams and concentrate H.sub.2 S for feed to a sulfur recovery plant.